Most bipolar cells and some horizontal cells termed the C-type respond to one mode of stimulus with hyperpolarization but respond to another mode of stimulus with a depolarization. Two major types are known in bipolar cells, which are on-center/off-surround type and off-center/on-surround type, and each of these types if further divided into subtypes, color coded and non-color coded. Accordingly, the patterns of hyper- and depolarization of individual cells are not simple, but nevertheless our previous studies suggest that sodium ions play an important role in the generation of both hyper- and depolarization responses. The proposed project is to study how far and how strict the sodium hypothesis applies to each response. In our study of bipolar cells, the cells in the carp, frog and turtle are impaled by intracellular microelectrodes, either made single or double-barreled according to the purpose of experiment. In each bipolar cell response we determine spectral characteristics, changes in input resistance during light with a bridge circuit. All these measurements are made by changing the state of adaptation to dark and light to distiguish contributions of rods and cones, and by changing the state of adaptation to colors to distinguish contribution of different pigment cones. With regard to the ionic mechanism of horizontal cell response (S-potential), direct measurements are made of the dynamics of intracellular Na ion, K ion and Cl negative with ion-specific microelectrodes, utilizing the huge horizontal cells of the stingray and with carp horizontal cells as a control. Whenever necessary, the cell types are morphologically identified by strain with Procion Yellow.